#include <vector>
#include <string>
#include <unordered_map>
#include <algorithm>

using namespace std;


class Solution {
public:

    // 97. 交错字符串
    // https://leetcode.cn/problems/interleaving-string/
    bool isInterleave(string s1, string s2, string s3) {
        int m = s1.size(), n = s2.size();

        if (m + n != s3.size())
            return false;

        s1 = ' ' + s1, s2 = ' ' + s2, s3 = ' ' + s3;
        vector<vector<bool>> dp(m+1, vector<bool>(n+1));
        dp[0][0] = true;

        for (int i = 1; i<=m; ++i)
        {
            if (s1[i]==s3[i])
                dp[i][0] = true;
            else 
                break;
        }

        for (int j = 1; j<=n; ++j)
        {
            if (s2[j]==s3[j])
                dp[0][j] = true;
            else 
                break;
        }
        
        for (int i = 1; i<=m; ++i)
        {
            for (int j = 1; j<=n; ++j)
            {
                dp[i][j] = (s1[i] == s3[i+j] && dp[i-1][j])
                        || (s2[j] == s3[i+j] && dp[i][j-1]);
            }
        }

        return dp[m][n];
    }
};